The present invention relates to a method and apparatus for recognizing a paster portion of a web in a rotary press, in which a bonded portion (i.e., a paster portion) between new and old webs is recognized to detect predetermined areas in the downstream and upstream of this paster portion as printing defects, thereby automatically eliminating the predetermined areas.
FIG. 6 shows a paper pasting condition in a rotary press. Referring to FIG. 6, reference numeral 100 denotes an old roll; 200, a new roll; 100-1, an old web supplied from the old roll 100 to a printing unit; and 200-1, a new web to be supplied from the new roll 200.
A double-coated tape 200-2 is adhered to the leading web end of the new roll 200 such that the adhesive surface of the tape 200 is exposed. During feeding of the old web 100-1, when the diameter of the old roll 100 reaches the minimum diameter, the old web 100-1 is bonded to the new web 200-1 through the double-bonded tape 200-2 at a predetermined timing, and a knife mechanism 300 is actuated to cut the old web 100-1.
The end of the old web 100-1 cut by the knife mechanism 300 has a saw-toothed wave shape, as shown in FIG. 7A. The leading web end face of the new web 200-1 is straight, as shown in FIG. 7B. The old web 100-1 and the new web 200-1 may be bonded obliquely, as shown in FIGS. 8A and 8B, depending on the paper pasting condition.
When the old web 100-1 and the new web 200-1 are bonded as described above, a printing defect is formed due to the influence of a tension varying at the time of bonding.
For this reason, a bonded portion (to be referred to as a paster portion hereinafter) between the old web 100-1 and the new web 200-1 is found in the subsequent process, and start and end positions of the upstream and downstream printing defects of the paster portion as the boundary are found, thereby eliminating the found printing defects.
In the prior art, however, since the search and elimination of the printing defects with respect to the paster portion as the boundary are manually performed, they are time-consuming and cumbersome, thus overloading the operator.